This invention relates to a coating apparatus and the method of coating for coating a long-sized supporting member which is reversed and transported by a backup roll with a coating solution, and in particular, to a coating apparatus and the method of coating wherein defects owing to coating streaks are reduced and the uniformity of thickness of the coated film is improved.
Apparatus for coating a supporting member with a coating solution can be classified into two main groups from their method of coating. One is a group of a type wherein coating solution of an amount just enough for forming the film is extruded and put on a supporting member, and this group is consisted of coating apparatus of a xe2x80x9cpre-metering typexe2x80x9d represented by extrusion coating, slide-bead coating, curtain coating, etc., and the other group is consisted of xe2x80x9cpost-metering typexe2x80x9d apparatus of a type wherein a large amount of coating solution is put on a supporting member and excessive amount of liquid is scraped off by a blade, an air knife, a roll, a wire-bar, etc. The outline about the method of coating is described in detail in xe2x80x9cModern coating and drying technology: Edward D. Cohen and Edgar B. Gutoff (1992 VCH Publishers, Ins.)xe2x80x9d.
In the post-metering type coating, the precision in the thickness of the primary coated film which is extruded from the coating head in the coating width direction (the direction perpendicular to the progressing of coating) is not required because excessively put liquid is later scraped off for adjusting the thickness, but an apparatus for post-metering is additionally required and a high-quality coating can not so much be expected for the theoretical reason.
On the other hand, pre-metering type coating is advantageous for a high-quality coating; however, because the coating solution extruded from the coating head makes the coated film as it is extruded, a high precision in the uniformity of thickness of it in the coating width direction is required. It is mostly correct to regard the uniformity of the thickness of the coated film in the coating width direction as the uniformity of the distribution of the amount of the extruded coating solution in the coating width direction.
For a technology for improving the uniformity of the distribution of the amount of the extruded coating solution in the coating width direction, it has been proposed to make the slit gap of the coating head narrow. However, merely to make the slit gap narrow causes the slit portion to be subjected to an excessive pressure of the coating solution, which poses problems that it becomes difficult to feed out the coating solution, and that alien substances and dusts in the coating solution become easy to be caught there. Further, there has been also a problem that in proportion to the slit gap being made narrower, a higher precision in the slit gap is required, to cause the working of the coating head to be difficult. Besides, as a similar technology, it has been proposed a technology to make the slit length longer, but it has also problems that a high coating solution pressure is required in the same way, and that the working of the coating head is difficult.
In the publication of TOKKAIHEI 8-266979, it is disclosed a technology for achieving the uniformity of the thickness of the coated film by measuring and controlling the amount of pressure loss in the manifold of the coating head and the amount of pressure loss in the slit by using a pressure gauge, not by a technique only to make the slit gap narrow or only to make the slit length long. However, the definition of the pressure loss is not clear, and there is a problem that it is practically troublesome because it is necessary to carry out the adjustment of the amount of pressure loss during the coating by the use of a pressure gauge. Further, the coating method disclosed in the above publication is only for use in the case where the supporting member is thin, equal to or thinner than 10 xcexcm and coating is carried out wit h the supporting member being in a free-span state (a state where the supporting member is not held and transported as floating), and nothing is referred to about how it is in the method of coating capable of coating also a thick supporting member, wherein a supporting member is coated in the process of being held and reversed by a backup roll.
It is an object of this invention to provide a high-precision coating apparatus and the method of coating for coating a transported supporting member in the process of being held and reversed by a backup roll with a coating solution extruded from a coating head, wherein the uniformity of thickness of the coated film is achieved and defects owing to coating streaks are reduced.
The object of this invention can be accomplished by the following structures:
(1) A coating apparatus comprising a backup roll for holding and reversing a long-sized supporting member which is being transported continuously, a coating head for carrying out coating in the above-described process of reversing by extruding a coating solution onto said supporting member, and coating solution supplying means for supplying said coating solution to said coating head, wherein said coating head has at least one coating solution supplying opening for receiving said coating solution from said coating solution supplying means, a manifold connected to said coating solution supplying opening for extending coating solution in the coating width direction, and a slit connected to said manifold for extruding said coating solution, and said coating solution supplying opening and said coating solution supplying means are provided in a manner such that the supply of said coating solution to said manifold is made symmetrical in terms of the left and right sides with respect to the center of the coating width, and the relationship expressed by the inequality (1) is effective:
xe2x80x8310xe2x88x924 less than (L2R2G3)/(24MS3) less than 10xe2x88x922xe2x80x83xe2x80x83(1),
xe2x80x83where M, G, L, S, and R have following meanings respectively:
M: the slit length [mm],
G: the slit gap [mm],
L: the coating width [mm],
S: the cross-sectional area of the manifold [mm2], and
R: the circumferential length of the cross-section of the manifold [mm].
(2) A coating apparatus set forth in the above-described paragraph (1), wherein, for the aforesaid at least one coating solution supplying opening, one is provided at the center of the coating width of the aforesaid manifold.
(3) A coating apparatus set forth in the above-described paragraph (1), wherein, for the aforesaid at least one coating solution supplying opening, one is provided at each of the both ends of the coating width of the aforesaid manifold, and one half of the total amount of flow of the coating solution is supplied to each of said coating solution supplying openings from the aforesaid coating solution supplying means.
(4) A coating apparatus comprising a backup roll for holding and reversing a long-sized supporting member which is being transported continuously, a coating head for carrying out coating in the above-described process of reversing by extruding coating solution onto said supporting member, and coating solution supplying means for supplying said coating solution to said coating head, wherein said coating head has at least one coating solution supplying opening for receiving said coating solution from said coating solution supplying means, a manifold connected to said coating solution supplying opening for extending said coating solution in the coating width direction, and a slit connected to said manifold for extruding said coating solution, and said coating solution supplying opening and said coating solution supplying means are provided in a manner such that the supply of said coating solution to said manifold is made asymmetrical in terms of the left and right sides with respect to the center of the coating width direction, and the relationship expressed by the inequality (2) is effective:
5xc3x9710xe2x88x924 less than (L2R2G3)/(6MS3) less than 5xc3x9710xe2x88x922xe2x80x83xe2x80x83(2),
xe2x80x83where M, G, L, S, and R have following meanings respectively:
M: the slit length [mm],
G: the slit gap [mm],
L: the coating width [mm],
S: the cross-sectional area of the manifold [mm2], and
R: the circumferential length of the cross-section of the manifold [mm].
(5) A coating apparatus set forth in (4), wherein said coating solution supplying opening is provided by one piece at one end of the coating width direction of said manifold.
(6) A coating apparatus set forth in any one of the above-described paragraphs (1) to (5), wherein the aforesaid manifold has the cross-section having a shape of a circle or a semicircle.
(7) A coating apparatus set forth in any one of the above-described paragraphs (1) to (6), wherein the cross-sectional area of the aforesaid coating head is equal to or larger than ten times the cross-sectional area of the aforesaid manifold.
(8) A coating apparatus set forth in any one of the above-described paragraphs (1) to (7), wherein a reduced pressure chamber is provided at the upstream side of the aforesaid coating head with respect to the transporting of the aforesaid supporting member which is being transported continuously.
(9) A coating apparatus set forth in the above-described paragraph (8), wherein the relationship expressed by the inequality (3) is effective:
xcex94P less than (6xcexcMQ)/(5LG3)xe2x80x83xe2x80x83(3),
xe2x80x83where M, G, L, Q, A, and AP have the following meanings respectively:
M: the slit length [mm],
G: the slit gap [mm],
L: the coating width [mm],
Q: the amount of supply of the coating solution [cc/min],
xcexc: the viscosity of the coating solution [Paxc2x7sec], and
xcex94P: the extent of reduction of pressure [Pa].
(10) The method of coating for carrying out coating by using any one of the coating apparatus set forth in the above-described paragraphs (1) to (9).